In one aspect, the invention relates to a composition of matter which has been provided with EMI shielding. In another aspect, the invention relates to a process for imparting EMI shielding to a nonconductive substrate sheet or support. In yet another aspect, the invention relates to a method for improving the shielding capability of a given quantity of EMI shielding material.
For many applications, it is desirable to provide finished parts with electromagnetic interference (EMI) shielding characteristics. In the automotive field, EMI shielding is required for plastic hoods, fenders, and firewalls. Office business machines require some form of shielding over parts of their internal areas. By regulation, emissions from all digital computing devices must be within certain radiation limits. Regulation of emissions is necessary because of increasing complaints of electrical malfunctions caused by electromagnetic interference. Examples include TV interference, flight instrument malfunctions caused by pocket calculators and activiation of electrically controlled devices by citizens band radios.
Several methods are known for providing EMI shielding of electronic components. Presently known methods include silver paint application, nickel paint application, conductive filler utilization, silver reduction, cathode sputtering, foil application, copper paint, vacuum metalizing, electroplating, flame/arc spraying and graphite paint application. With the exception of conductively filled plastics, all of the shielding methods suffer from either a limited life due to chipping, cracking, peeling or they involve costly secondary operations.
The most desirable method of providing shielding is with conductively filled plastics because the shielding material is an integral part of the plastic and will not chip or blister and does not require secondary operations to apply. A problem is that incorporating conductive fillings into plastics frequently reduces product properties to an unacceptable extent because of the high amount of filler required to provide acceptably high shielding characteristics and the relatively low reinforcing characteristics of most fillers. It would clearly be desirable to provide a technique so that acceptable shielding is obtainable with lower amounts of filler and the filler imparts good reinforcement to the part.